Example of a severely dunted cone 6 stoneware tile. This problem was deliberately created by stacking several tiles on top of this one. This set up a temperature gradient across it so that different parts passed through quartz inversion at different times.
Dunting generally refers to firing cracks that occur in ceramic ware as it is cooled in the kiln. The reason is generally uneven cross section or too rapid cooling.
In ceramics, this refers to the sudden volume change in crystalline quartz particles experience as they pass up and down through 573C. Fired cracks are often related to this.